Gravity waves and the aether

[Strange]

.

 

 

No ! For me there are too many ' everything is everything ' ,

 

I need to know what is the source of what ?

 

Otherwise it's like "trying to pick yourself up by your own bootstraps " as we said in olden days .

Perhaps " lift yourself up by pulling on your shoe laces " would be a today's translation .

 

Mike

 

It is just a case of different words ("gravity" or "space-time curvature") describing the same thing.

 

No bootstraps required. Space and time exist. Mass and energy exist. Space-time is affected by mass and energy.

 

If you want to know why those things exist and why they affect each other in that way, well ... that's the way god planned it, I guess. (And you can choose whether "god" means a divine being or just "the laws of nature").

[Mike Smith Cosmos]

It is just a case of different words ("gravity" or "space-time curvature") describing the same thing.

 

No bootstraps required. Space and time exist. Mass and energy exist. Space-time is affected by mass and energy.

 

If you want to know why those things exist and why they affect each other in that way, well ... that's the way god planned it, I guess. (And you can choose whether "god" means a divine being or just "the laws of nature").

.

Let's just take a ' rain check on that sequence ?

 

You are saying :-

 

 

First : divine being or just laws of nature ?

 

Second : mass and energy from somewhere .?

 

Third : space time affected . from ?

 

Forth : space time curvature , / Gravity ?

 

 

Not sure wether this is in the order you mean ( different or concurrent ) ? Or where all this inter galactic stuff comes from that gives space curvature , and where it comes from ? One , two, three or four .

 

Mike

Edited July 6, 2016 by Mike Smith Cosmos

[Strange]

Two, three and four are all a consequence of one.

There is no order among them.

[geordief]

What is "there" is the distance between those particles, grains of dust, etc. That is what changes.

Assuming there is a gravitational field does this distance you described mean a spacio-temporal distance or (since you are here describing the particles without a direct reference to their place in time) is it ,on this occasion just the spacial distance you explicitly meant?

 

If I have understood GR correctly ,it is my understanding that the spacio-temporal distant does not change but I am not quite sure if this unchangeability of "distance" within the manifold applies to a curved spactime as well as it does to a flat spacetime.

 

Also not sure about by use of "spacio" from a simple language point of view

[MigL]

Mike, if you expect Strange to hand you a 'clump' of space-time, that's not gonna happen !

 

Space-time is the geometry of the universe in three dimensions of space and one of time.

A map of events, if you will.

As Mordred explained, a contour map is modified by elevation to show a 'curvature'. This curvature is evident by the co-ordinates of the map having reduced or increased separation.

And as Markus explained ( much better than I did ) space-time geometry is modified by mass-energy to show a 'curvature' ( in 4D this time ). This curvature ( the changed separation between events in space-time ) is what we call gravity.

 

( I was glad that you picked up on the Equivalence Principle between acceleration and gravity )

Edited July 6, 2016 by MigL

[Markus Hanke]

My understanding was that the manifold that modeled spacetime was that with the parameters (correct terminology?) of 3 spatial and one temporal(sign reversed ) components -a hyperbolic manifold.

Are there are ways (manifolds) of modeling spacetime ?

 

Yes, that's right. The term you were looking for is "metric signature", and only manifolds with a signature of (+,-,-,-) or (-,+,+,+) are useful models for spacetime.

Purely mathematically though, you can of course have many other types of manifolds - the Euclidean space we are all familiar with from high school geometry is an example. Or you could consider a manifold with two time directions, like (-,-,+,+). But those are not suitable models for spacetime, because they don't accurately reflect how events in the real world are related.

[Strange]

Mike, if you expect Strange to hand you a 'clump' of space-time, that's not gonna happen !

 

Damn. There goes that money-making scam scheme!

 

How about a hole? Anyone want to buy a hole?

[Mike Smith Cosmos]

 

( I was glad that you picked up on the Equivalence Principle between acceleration and gravity )

With the stone in the aeroplane seat . Yes it was great .

 

I also tried to drop a concrete lemon and a fresh picked lemon , exactly alike , from the top of the leaning tower of Pisa.

Although a local Italian helped . They would not let people with heavy objects up the tower . So I did it from the top of a nearby Piza Hotel . I thought Italy was the home of science. However my wife did think I was crazy . By the way both lemons were recorded reaching the ground at the same time ! ..the effect of Gravity is acceleration ..

 

Now this series of steps to see what is actually out there . 1,2,3,4

 

My guess is " the universe has inbuilt acceleration " in other words it's either falling inwards fast , flying outwards fast , or spinning ?

Edited July 6, 2016 by Mike Smith Cosmos

[geordief]

 

Damn. There goes that money-making scam scheme!

 

How about a hole? Anyone want to buy a hole?

Space and Time Real Estate. I am sure you might get a few nibblers.

 

Haven't people sold plots of land on the Moon already?

 

https://www.moonestates.com/

 

http://www.scambusters.org/landonthemoon.html

Edited July 6, 2016 by geordief

[Mike Smith Cosmos]

Mike, if you expect Strange to hand you a 'clump' of space-time, that's not gonna happen !

 

Space-time is the geometry of the universe in three dimensions of space and one of time.

A map of events, if you will.

As Mordred explained, a contour map is modified by elevation to show a 'curvature'. This curvature is evident by the co-ordinates of the map having reduced or increased separation.

And as Markus explained ( much better than I did ) space-time geometry is modified by mass-energy to show a 'curvature' ( in 4D this time ). This curvature ( the changed separation between events in space-time ) is what we call gravity.

 

 

.

 

First Devine being or just laws of nature ?

 

Second : mass and energy from somewhere .?

 

Third : space time affected . from ?

 

Forth : space time curvature , / Gravity ?

 

Considering these events .

 

1. If I was going to create a universe , or I was just the laws of nature . I or It would need to make sure that something so large would not just dissipate to the four winds , . It would need some large , thorough inbuilt system to keep itself together . So something like gravity would be essential . Strong, far reaching and pervading everywhere.

 

2. These are the ingredients of the universe . Matter to be, to exist , to be real . Energy to do , to happen .

 

3. Space infers a place to do it or be done , Time is the scroll of destiny , when things happen .

 

4 . Curvature must have some connection with this link between gravity , spinning and acceleration . Maybe like ancient man thought he was on a flat earth , until we worked out it was curved and spinning . Maybe the same is True of space and the Universe , it's curved and spinning , and we don't realise it yet . One massive dust and grit filled sphere of matter spinning in a complex way .

 

 

I know these are a bit scant . But it might create a talking point , as we appear to be straying into areas , little known about .

 

Mike

Edited July 6, 2016 by Mike Smith Cosmos

[geordief]

.

 

First Devine being or just laws of nature ?

 

Second : mass and energy from somewhere .?

 

Third : space time affected . from ?

 

Forth : space time curvature , / Gravity ?

 

Considering these events .

 

1. If I was going to create a universe , or I was just the laws of nature . I or It would need to make sure that something so large would not just dissipate to the four winds , . It would need some large , thorough inbuilt system to keep itself together . So something like gravity would be essential . Strong, far reaching and pervading everywhere.

 

2. These are the ingredients of the universe . Matter to be, to exist , to be real . Energy to do , to happen .

 

3. Space infers a place to do it or be done , Time is the scroll of destiny , when things happen .

 

4 . Curvature must have some connection with this link between gravity , spinning and acceleration . Maybe like ancient man thought he was on a flat earth , until we worked out it was curved and spinning . Maybe the same is True of space and the Universe , it's curved and spinning , and we don't realise it yet . One massive dust and grit filled sphere of matter spinning in a complex way .

 

 

I know these are a bit scant . But it might create a talking point , as we appear to be straying into areas , little known about .

 

Mike

C'est magnifique ,mais ce n'est pas la .......... Science

 

You know I think it is a bit back to front. First we understand how things work and then we play around with how we describe them (there can be all sorts of ways I would guess)

 

If you look for analogies and try to make the world "fit them" then that is to expect the world to be like that "because we say so".

Edited July 6, 2016 by geordief

[Mordred]

 

Damn. There goes that money-making scam scheme!

 

How about a hole? Anyone want to buy a hole?

Well in Dungeons and Dragons. They have a magic item called a portable hole. Lol

 

Sorry off topic but I just couldn't help myself on that comment😈

Edited July 6, 2016 by Mordred

[Mike Smith Cosmos]

.

As with the electro magnetic field ,you guys helped me establish quite what was out there that the electro magnetic field could establishing itself in .

 

Now , I wish your help to tease out , what quite is out there , that the gravitational field , which you indicate has something to do with space itself .

 

But now we are talking of shapes , curves , measurable geodesic geometry . I need help to establish quite what the geometry is 'IN ' .or. 'ON'

 

Now I know you want to say it's just there, in space . But I need a bit more than that .

 

That is like saying I will draw a line in a vacuum . I need to 'pin you down ' a bit . With something I can identify with . Not just a mathematical operation ,something tangible . If you would not mind . Please .

 

There , I have asked nicely .

 

Is there any way the ' Higgs Field ' has anything to do with this ? Or was the gravitational field something that came out of the first break with supersymetry ?

 

Mike

Edited July 6, 2016 by Mike Smith Cosmos

[Mordred]

Is there any way the ' Higgs Field ' has anything to do with this ? Or was the gravitational field something that came out of the first break with supersymetry ?

 

Mike

Thats really one of those questions that we haven't been able to accurately answer yet. Theoretically gravity would symmetry break first. However in order for that symmetry break to occur a guage boson would need to drop out of thermal equilibrium.

 

Theoretically this would be the graviton. Which would then mean that the graviton would be the heaviest boson in the total energy equivalent.

If that turns out to be the case then gravity would be considered a force in every aspect.

 

Without the graviton were stuck with gravity as a result spacetime geometry. More accurately the influences upon the stress-momentum tensor. This tensor can be influenced by any and all other particle to field relations.

In this sense it the sum of all field interactions. Rather than its own unique field. (Bit of an oversimplification) but I know how much you don't see math relations.

 

We won't know until we can quantize gravity. Or produce a graviton at an accelerator.

 

Gravity exists before the Higgs symmetry breaks. In some books a fully unified field has been called super gravity.

[MigL]

We previously took advantage of Quantum Field Theory for the EM field, since the all-pervasive QED field gives rise to the associated particles via the Dirac equation and relativistic Shroedinger equation, just to satisfy your need to have 'something to pin it on'.

And we could use the color field of QCD similarly for the strong force.

But I'm afraid we can't help you with gravity,Mike.

We don't have a quantum field theory for gravity, all we have is a classical geometric theory.

For now, you're going to have to be satisfied with 'the geometry is the field'.

Pin it wherever you'd like.

[Mordred]

Is there any way the ' Higgs Field ' has anything to do with this ? Or was the gravitational field something that came out of the first break with supersymetry ?

 

Mike

Thats really one of those questions that we haven't been able to accurately answer yet. Theoretically gravity would symmetry break first. However in order for that symmetry break to occur a guage boson would need to drop out of thermal equilibrium.

 

Theoretically this would be the graviton. Which would then mean that the graviton would be the heaviest boson in the total energy equivalent.

If that turns out to be the case then gravity would be considered a force in every aspect.

 

Without the graviton were stuck with gravity as a result spacetime geometry. More accurately the influences upon the stress-momentum tensor. This tensor can be influenced by any and all other particle to field relations.

In this sense it the sum of all field interactions. Rather than its own unique field. (Bit of an oversimplification) but I know how much you don't see math relations.

 

We won't know until we can quantize gravity. Or produce a graviton at an accelerator.

 

Gravity exists before the Higgs symmetry breaks. In some books a fully unified field has been called super gravity.

 

A system of nothing but photons can generate gravity. When all particles are in thermal equilibrium. There is no way to distinquish any particle from a photon.

This condition exists prior to the Higgs field symmetry break.

Edited July 6, 2016 by Mordred

[disarray]

I am wondering whether, in terms of the spacetime model, whether the word "time" itself is not misleading: Isn't the so-called "curvature" of space enough to explain the apparent time dilation effects that have been detected? For a lay person such as myself, one might ask whether time just "seems" to slow down under certain conditions (e.g., depending upon distance from earth) because everything in a clock slows down (not to mention the rate of cell divisions).

 

I have read a couple of places that photon clocks, unlike atomic clocks, are not affected by gravity or whatever with respect to time dilation....true or false?

 

Perhaps one might use the term "curved space" instead of "spacetime." Could we not also use a term such as "compression" to refer to the fact that things slow down in space, just as someone walks more slowly when in shallow water? Doesn't the term "compression" make more sense in terms of explaining how gravity is found everywhere on our spherical planet....seems hard to envisage space bending entirely around a sphere. Light bending as it passes the sun seems to be a pretty literal example of spacetime curvature....so then wondering why scientists say, no, the term "curvature" is just an expression that is used to explain the measurements, but shouldn't be taken in the usual sense of the word.

 

In general, I get the feeling that lay persons are less concerned with whether or not scientific models (e.g., Theory of relativity) come up with workable measurements, than they are with getting some sort of metaphor that will help them partially understand what seems counterintuitive and that can not be visually modeled. (As an aside, i recall reading that Einstein said when asked what might be unusual about the way he thought, he replied that he thought in terms of "more or less distinct visual images.")

Edited July 6, 2016 by disarray

[Markus Hanke]

 

 

For a lay person such as myself, one might ask whether time just "seems" to slow down under certain conditions (e.g., depending upon distance from earth) because everything in a clock slows down (not to mention the rate of cell divisions).

 

That is not what happens. Time dilation is a relationship between different clocks in spacetime, it is not a physical "change" of some sort that "happens" to a clock.

 

 

 

I have read a couple of places that photon clocks, unlike atomic clocks, are not affected by gravity or whatever with respect to time dilation....true or false?

 

False. Two photon clocks at different places, when compared, are subject to time dilation just like any other type of clock. There's nothing particularly special about light at all.

 

 

 

Perhaps one might use the term "curved space" instead of "spacetime."

 

You can't eliminate time out of the equation. In fact, it is the principle of extremal ageing which determines most of the dynamics of GR, i.e. the behaviour of test particles under the influence of gravity. The geodesic equation is nothing other than a mathematical statement of that principle. Also, remember that locally your theory must reduce to Special Relativity, so time is an integral part.

 

 

 

Could we not also use a term such as "compression" to refer to the fact that things slow down in space

 

That doesn't make any sense, I'm afraid.

 

 

 

so then wondering why scientists say, no, the term "curvature" is just an expression that is used to explain the measurements, but shouldn't be taken in the usual sense of the word.

 

The curvature in your example is just the relationship between different events along the light beam. There is no mechanical "bending" involved, since the light is not subject to acceleration at any point on its trajectory.

 

 

 

getting some sort of metaphor that will help them partially understand what seems counterintuitive

 

I have tried this for literally years when I first learned GR, and I can assure you that this won't work, because all analogies are necessarily limited and severely flawed. GR seems counterintuitive to many people precisely because they get stuck thinking in terms of analogies, not because the model itself is in any way extraordinary. Ultimately - and I might make myself unpopular by saying this - the only way to understand GR is to actually abandon all visualisation aids and analogies, and go and learn the mathematics behind it. The point here is that there is no need to master those mathematics - you need to only get to a level where you can understand their meaning, so complete mastery isn't required. That is perfectly achievable for the vast majority of people, even those who aren't mathematically inclined, but it does take patience, effort, and perseverance.

 

The answer is - the metaphor you are looking for simply does not exist. You cannot capture all relevant aspects of a non-trivial 4-dimensional concept by drawing pictures on a screen; sometimes even I wish that was possible, but the raw truth is that it's not. Yes, you can come up with certain visualisation aids for certain aspects of the model, but it is crucially important to understand the limitations of those analogies - and that's where a lot of people fall down, and where the "counter-intuitiveness" comes in. They confuse the analogy with the model itself. GR is not a rubber sheet, it is not an expanding loaf, and it is not ripples on a pond. Full GR is simple geometry, but it is not the geometry we are used to from everyday human experience, but a generalisation of it.

usual sense of the word

 

I should explicitly point out here that the "usual sense of the word" curvature is not the type of curvature that is used in GR at all. When the average person on the street mentions curvature, then the mental image that is invoked is one of some kind of embedded surface bending within a higher-dimensional space - like the surface of a 2-sphere bending in 3-space for example ( that's where the rubber-sheet analogy comes from ). This type of curvature is called extrinsic curvature. However, GR uses an entirely different notion, called intrinsic curvature - this is defined by what happens when you transport tangent vectors along closed curves. This type of curvature is called "intrinsic", because it makes no reference to any embedding into higher-dimensional spaces, or any measurements that are external to the manifold itself. Instead, it is entirely determined by the measurements within the manifold. There is no good way to visualise this, and if one tries to force the issue, then that's where the counter-intuitiveness comes in. For example, people see a cylinder, and they intuitively say "oh, that's curved !"; and so far as extrinsic curvature is concerned, that is correct. However, GR considers only the intrinsic geometry of the surface, and it turns out that the surface of cylinder has no intrinsic curvature at all - it is perfectly flat, and that is true whether or not the cylinder is embedded anywhere. People find that counter-intuitive, but only because they do not know the correct meaning of "curvature". Hence, the only way to really understand GR is to go away from the analogies and visualisations, and learn the actual meaning behind it.

[disarray]

That is not what happens. Time dilation is a relationship between different clocks in spacetime, it is not a physical "change" of some sort that "happens" to a clock.

I have read something to the effect that "Clocks just tick slower in a deeper gravity well. Hearts beat slower. Synapses fire slower. Food is digested slower. Lungs extract air slower. Molecules move slower. DNA breaks down slower. Absolutely every single thing happens more slowly when in a deeper gravity well."

 

This was the sort of thing I am referring to when I suggested that "time" is just an umbrella term that describes how things "happen" more slowly in comparison with similar clocks or people elsewhere.

In short, it seems to me that "time" is synonymous with "happening." If the twin who returns in the spaceship really is younger than the one that stayed on earth when they shake hands, we can't just say that time dilation is a relative/observational phenomena....the aging is real.

[ajb]

I have read something to the effect that "Clocks just tick slower in a deeper gravity well. Hearts beat slower. Synapses fire slower. Food is digested slower. Lungs extract air slower. Molecules move slower. DNA breaks down slower. Absolutely every single thing happens more slowly when in a deeper gravity well."

When viewed from 'far away' - as far as the person in the well nothing changes for his/her clocks. You only get time dilation effects when one compares clocks.

[geordief]

When viewed from 'far away' - as far as the person in the well nothing changes for his/her clocks. You only get time dilation effects when one compares clocks.

If you have 2 observers ,one of whom is in a gravitational well and the other not is it correct to say that the observer in the gravitational well will see the other observer "speeded up"?

 

An vice versa (in a different way from in special relativity where both observers see the other as "slowed down" )

 

Going down a gravitational well in that case (if I was right) reminds me a bit of "going into hibernation".

 

I wonder if a probe was sent to the surface of Jupiter whether any noticeable such effects might occur (not that I understand Jupiter is very dense,less than 3 times that of the Earth I think.)

 

I have read something to the effect that "Clocks just tick slower in a deeper gravity well. Hearts beat slower. Synapses fire slower. Food is digested slower. Lungs extract air slower. Molecules move slower. DNA breaks down slower. Absolutely every single thing happens more slowly when in a deeper gravity well."

I don't think the speed of light changes in a gravitational well,dies it?

[ajb]

If you have 2 observers ,one of whom is in a gravitational well and the other not is it correct to say that the observer in the gravitational well will see the other observer "speeded up"?

When they compare clocks - how they do this is another question- the observer in the well will see that the clock of the distant observer has been 'running faster'.

[geordief]

When they compare clocks - how they do this is another question- the observer in the well will see that the clock of the distant observer has been 'running faster'.

Does that represent a practical difficulty? Don't the measurements from Juno take into account the gravitational well?

[disarray]

When viewed from 'far away' - as far as the person in the well nothing changes for his/her clocks. You only get time dilation effects when one compares clocks.

That seems like you are suggesting that the younger spaceship twin will only notice that his earthbound twin has more wrinkles when he gets back to earth and compares complexions. This suggests that they looked the same until they met up.

 

Or, the equivalent, that a person living near the dead sea will only notice that his twin living in the Himalayas has (slightly) more wrinkles (for arguments sake...I doubt any difference would be perceptible) when they meet up for the first time since childhood fifty years later. Again, this suggests that they looked the same until they met up.

 

Surely such ageing is real and continuous (e.g., during all the time that the twins were separated), and not just a matter of people observing time differently depending upon their frame of reference, or of their suddenly ageing when they meet up or compare clocks.

Edited July 7, 2016 by disarray

[ajb]

Does that represent a practical difficulty? Don't the measurements from Juno take into account the gravitational well?

If they agree on a wavelength of a light bean sent between the two they could look for gravitational Doppler shift. Or if they send pulses they could agree on the rate they are sent at.

 

I doubt there is must effect for probes like Juno - though I am not sure how accurate they need the timing to be.

 

 

For sure it is important for the GPS system.

 

That seems like you are suggesting that the younger spaceship twin will only notice that his earthbound twin has more wrinkles when he gets back to earth and compares complexions.

They have to compare clocks somehow - otherwise the notion of time dilation makes no sense. It does not mean that they actually have to physically meet, only that they need some way of comparing clocks.